Military officials announced the deaths of six more U.S. troops in the recent violence, bringing to 11 the number of Americans killed on the same day.
In Baghdad's Sadr City slum and in its northern Kazimiyah suburb, thousands of angry Shiites rallied to condemn twin suicide attacks Thursday that killed at least 136 people, including the U.S. troops.
The protesters also denounced what they claimed was American backing for Sunni Arab politicians who have supported insurgent groups and are now protesting that last month's elections were tainted by fraud.
Final results from the Dec. 15 elections could be released next week and they are expected to show the religious Shiite United Iraqi Alliance with a strong lead. The Shiites will, however, need to form a coalition government with support from Kurdish and Sunni political groups.
The rallies and threats by Iraq's largest Shiite religious party to react with force if the militant attacks continue have renewed fears that paramilitary militias - now thought to make up part of some elite police units- would take to the streets and carry out reprisals.
In Sadr City, more than 5,000 demonstrators chanted slogans in favor of the Interior Ministry and against U.S. Ambassador Zalmay Khalilzad. But they reserved most of their ire for hard-liners such as Saleh al-Mutlaq, the outspoken head of the Sunni Arab National Dialogue Front.
''We're going to crush Saleh al-Mutlaq with our slippers,'' they chanted, many armed with automatic weapons.It is an insult in Arab culture to touch someone with shoes, which are considered unclean.
Al-Mutlaq denounced what he called ''irresponsible statements'' and condemned terrorist attacks.
''No government post is worth a single drop of Iraqi blood,'' he told The Associated Press. ''Our decision to join the political process means that we reject terrorism.''
Western experts said more violence was inevitable in coming weeks.
''I can't imagine that we are going to get to a constituted government before more violence, more bluffing, more slamming of doors. This is for all the marbles, and people are going to play a tough game,'' said Jon Alterman, a Middle East expert at the Center for Strategic and International Studies in Washington.
Moderate Shiite leaders, including Iraq's most prominent cleric Grand Ayatollah Ali al-Sistani, called for cooperation.
''Sunnis and Shiites are brothers under one sky,'' Sheik Ali Al-Fatlawi, an al-Sistani representative, said in a sermon at the Imam Hussein shrine, in the Shiite holy city of Karbala south of Baghdad. ''We are demanding that politicians give up their selfishness and take care of their people.''
A suicide blast Thursday near the shrine killed 63 people and wounded 120. That day's other suicide attack took place in Ramadi, west of Baghdad, and killed 58. A U.S. Marine and soldier died in the Ramadi attack, in which the bomber infiltrated a line of police recruits. Two soldiers were also killed near Baghdad when their vehicle hit a roadside bomb. Two U.S. Marines were killed by separate small arms attacks during combat operations in Fallujah.
